1. Field of the Invention
This invention relates to a process for preparation of vinyl chloride polymers such as polyvinyl chloride, and more particularly to a process for preparation of a vinyl chloride polymer having a narrow distribution of particle size and capable of being processed into products having few fish-eyes.
2. Description of the Prior Arts
A process for preparation of vinyl chloride polymers by dispersing vinyl chloride or a vinyl monomer mixture comprised mainly of vinyl chloride in an aqueous medium by use of a suitable dispersant and subjecting the resultant dispersion to suspension polymerization by use of an oil-soluble catalyst is disclosed, for instance, in "Polyvinyl Chloride-Its Chemistry and Industry-III", edited by Kinki Chemical Industry Association, Vinyl Section, and published from Asakura Publishing Co., Ltd. on Jan. 20, 1969. The process is now widely practiced on an industrial scale.
Also, Japanese Patent Publication (KOKOKU) No. 63-56245 (1988) discloses a process for preparation of a vinyl chloride polymer in which high-speed shear agitation is applied to a polymerization reaction system, followed by suspension polymerization.
In the above processes for preparation of vinyl chloride polymers, however, the use of not less than 0.5% by weight of dispersant based on the monomer is indispensable. If the amount of the dispersant is decreased, the resultant vinyl chloride polymer particles will be coarser and have a broader distribution of particle diameter. Furthermore, the so-called polymer scale will be deposited on the walls of the polymerization vessel, and the deposited scale may peel off to mix into the reaction product, causing fish-eyes and a lowered product quality.
In addition, the process for preparation of a vinyl chloride polymer disclosed in Japanese Patent Publication (KOKOKU) No. 63-56245 (1988) is applied to the preparation of vinyl chloride polymers for paste resin use, particularly. That is to say, the process is for preparing vinyl chloride polymers with an extremely small particle diameter of from several micrometers to several tens of micrometers, and is different from the general suspension polymerization process for preparation of vinyl chloride polymers 100 to 200 .mu.m in particle diameter.